Air pressure reading within a tornado

Has anyone ever theorized just how low the adjusted sea level air pressure drops to within a tornado?

Is the pressure lowest right at the surface, or is it higher aloft?

I did a little looking around on the web, but didn't really find very much info.
Tim Samaras's probes have captured some data on this... I believe his Manchester, SD, deployment recorded a 100mb pressure deficit as the tornado moved over the probe. Could throw some numbers into a cyclostrophic flow equation to come up with an 'idealized' pressure deficit for a given wind/flow field I suppose.
Wow, that was some interesting information. Thanks for the links guys!

A 100mb drop is unbelievable. I guess I can see how that may cause the "ear popping" that is sometimes reported by tornado victoms.